1. Field
Example embodiments relate to a semiconductor light emitting device. Other example embodiments relate to a highly transmissive optical thin film having an improved structure, in which, optical reflection (due to a difference in the refractive index between a semiconductor material and the air, when light is extracted from a semiconductor light emitting device into the surrounding medium (e.g., an encapsulation material)) may be suppressed, an optical output loss may be reduced and light transmittance efficiency may be maximized or increased, and a semiconductor light emitting device having the same. Other example embodiments relate to methods of fabricating the same.
2. Description of the Related Art
Light emitting devices, for example, light emitting diodes (LEDs), are basically semiconductor PN junction diodes. Silicon PN junction plays a leading role in the electronic information revolution, and a PN junction of a III-V-group compound semiconductor plays a leading role in the optical technology revolution. The III-V-group compound semiconductor may be made by combining III- and V-group elements of the periodic table of elements. III-V compounds may have an advantage of increased electrical-to-optical-conversion efficiency that may be close to about 100%. This efficiency may be about one thousand times higher than the efficiency of silicon. LEDs may be widely used in light emitting devices, from the initial stage of development of a material and may play a leading role in the optical revolution. Because III-V compounds have an increased electron speed at a given electrical field and may operate at an increased temperature, III-V compounds may be widely used in high-speed and high-power electronic devices. For example, several III- and V-group elements may be combined so that a semiconductor having a variety of material compositions and characteristics may be manufactured.
Basic characteristics of an LED are luminous intensity (units: candela (cd)), used for an LED emitting in the visible wavelength region and radiant flux (units: watt) used for LEDs irrespective of their emission region. Luminous intensity is indicated by light intensity per unit solid angle, and luminance (brightness) is indicated by luminous intensity per unit area of the emitting LED chip. A photometer may be used to measure the luminous intensity. Radiant flux may represent all power radiated by an LED, irrespective of wavelengths and may be represented by the energy radiated per unit time.
The main factors for determining a visible-spectrum LED performance may be the luminous efficiency indicated by lumen per watt (lm/W). This may correspond to the wall-plug efficiency (optical output power divided by electric input power) and may include consideration of the human eyes' luminosity factor. Luminous efficiency of an LED may be determined by three factors, for example, the internal quantum efficiency, light-extraction efficiency, and the operating voltage. Much research is currently devoted to the improvement of the luminous efficiency of LEDs.
In general, conventional III-V nitride LEDs may have a sapphire/n-type GaN/multiple-quantum well (MQW) active region/p-type GaN structure. However, in conventional LEDs having such a structure, there may be limitations when addressing current technical objectives, for example, a first objective is improving the internal quantum efficiency of an MQW active region and a second objective is the manufacturing of high-power LEDs. Accordingly, the structure of an LED needs to improve so that the limitations may be overcome and the efficiency of LEDs may be increased.